The present invention relates generally to a method for processing seismic data. More particularly, the present invention provides a method for recursively, continuously estimating the noise and signal components of seismic trace signals. Additionally, the present invention discloses a method for suppressing the noise component of a seismic trace signal so as to enhance the signal component thereof. A measure of the signal component of a first seismic trace signal is obtained. Recursively, a measure of the signal component of a second seismic trace signal is obtained employing the measure of the signal component of the first seismic trace signal.
Seismic exploration involves generating seismic waves at the surface of the earth by means of a seismic source. The seismic waves travel downwardly into the earth and are reflected and/or refracted due to differences in elastic properties at the interface of various subterranean formations. Detectors, called seismometers, or geophones, located along the surface of the earth and/or in a borehole, produce analog electric seismic signals or seismic trace signals in response to detected seismic wave reflections and/or refractions. The analog electric seismic signals or seismic trace signals from the seisomometers, or geophones, can then be recorded. Alternatively, the analog seismic signals or seismic trace signals from the seismometers, or geophones, can be sampled and digitized prior to being recorded. The seismic data recorded in either manner are subsequently processed and analyzed to determine the nature and structure of the subterranean formations.
In many seismic operations, low energy seismic sources, such as vibrators, are employed resulting in the signal component of a resulting seismic trace signal being low in amplitude compared to the noise component thereof. Low energy seismic sources, such as vibrators, generate a chirp signal of seismic energy. In the case of low energy seismic vibrators, the recorded seismic wave reflections and/or refractions can be cross-correlated with a replica (called the pilot signal) of the original chirp signal in order to reproduce recordings similar to those which would have been produced with a high energy seismic source. Unfortunately, the recorded seismic data always includes some unwanted noise in addition to the detected seismic waves reflected and/or refracted from the subterranean formations which noise can distort or even ruin the seismic data by obscuring seismic events related to the reflections and/or refractions from the subterranean formations. Noise is generally nonrecurring or not dependent upon the seismic vibrator. The noise appears in many forms, such as atmospheric electromagnetic disturbances, wind, motor vehicle traffic in the vicinity of the prospect area, recorder electrical noise, etc. When a high energy source is used, such a dynamite, the level of the detected seismic signal component is usually much greater than the noise component. In spite of the unfavorable relationship between the noise component and signal component of a seismic trace signal generated by a low energy seismic source, it has been determined that seismic trace signals having such poor signal-to-noise character can be combined or vertically stacked in such a fashion that the signal component will be reinforced while the noise component will tend to be cancelled out.
In the present invention, the resolution of seismic event in the signal component in a seismic trace signal can be favorably enhanced by recursively determining the noise component therein by estimating that the signal component of a second seismic trace signal is approximately equal to the signal component of a first seismic trace signal.